Any HGTV addict (House Hunters, anyone?) knows that choosing the right home can be a riveting decision: your future happiness could hinge on those marble countertops or high ceilings! But for the rest of us, don’t despair: chemistry is here with a new smart window coating guaranteed to lift your mood!

A recently-published study in Nature Communications demonstrates a material (Fc-gel-EGP6) that serves double duty as a smart window coating. Not only does the coating transmit less IR light at higher temperatures, keeping your home cool in the summer— it can also transition from cool color tones in the hot summer to warm color tones in the dark and cold of winter.

Figure 1. Left: Repeat unit of the ferrocene-polyacrylamide gel. The orange shape is a visualization of ferrocene, which absorbs orange light in its reduced form; Right: ethylene glycol-modified pillar[6]arene. The grey shape is a visualization of EGP6, which forms a cylindrical structure. Reprinted (adapted) with permission from Wang et al, Nature Comm. 2018, 9, 1737.

Fc-gel-EGP6 is fundamentally a composite of a thermoresponsive polymer, ethylene glycol-modified pillar[6]arene, and a redox-active molecule, ferrocene, attached to a second polymer composed of polyacrylamide (Figure 1). When the two polymers are mixed, the ferrocene molecules nest inside the cylindrical structure of EGP6 (Figure 2) in a process called host-guest complexation.

Figure 2. Fc-gel-EGP6, with ferrocene (orange) shown mixed into EGP6 (grey). As ferrocene is oxidized to ferrocenium, the color of the composite transitions from yellow to green. Reprinted (adapted) with permission from Wang et al, Nature Comm. 2018, 9, 1737.

An electric potential applied to the composite – perhaps by a switch at the edge of your window – oxidizes ferrocene to ferrocenium and gives the window a greenish tint (Figure 3).

Figure 3. Fc-gel-EGP6, with ferrocene (orange) shown mixed into EGP6 (grey). As ferrocene is oxidized to ferrocenium, the color of the composite transitions from yellow to green. Reprinted (adapted) with permission from Wang et al, Nature Comm. 2018, 9, 1737.

For those of you who don’t remember your Pantone color wheel, “cool tones” include green, blue and purple, while “warm tones” are red, orange and yellow. Research in the social sciences has shown that different colors of light can affect your emotions and mood; light therapy is already being used as a treatment for that classic winter malady, seasonal affective disorder (SAD).1 A single molecule like ferrocene, absorbing a limited range of light, might not offer the color tones to perfectly complement your wallpaper; however, ferrocene does absorb blue light, which heightens your emotional response to stimuli.1

So far, the Fc-gel-EGP6 coating has only been tested for approximately one hundred cycles of temperature and of electric potential, so don’t expect to see these windows on homes just yet! But the chemistry underlying this novel technology may someday be keeping your home cool— and your emotions even cooler.